Finned heat exchange tube and process for forming same

ABSTRACT

A finned heat exchange tube includes a metal cylindrical central tube having an outer surface and a metal fin helically disposed on and in thermally conductive contact with the outer surface of the tube. The cross-section of the fin is trapezoidal in shape, with a longer and a shorter base, the longer base being in contact with the outer surface of the tube. Alternatively, the fin can have a cross-section substantially rectangular in shape, having rounded comers and sides of longer and shorter dimensions perpendicular to one another, a side of the shorter dimension being in contact with the outer surface of the tube. A process for forming a heat exchanger tube comprises helically winding and securing a metal fin on an outer surface of a metal cylindrical central tube. The fin, which is in thermally conductive contact with the central tube, has a cross-section that can be trapezoidal or substantially rectangular in shape.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is related to and claims priority fromProvisional Application Serial No. 60/230,245, filed Sep. 1, 2000 byDavid F. Fijas for FINNED HEAT EXCHANGE TUBE AND PROCESS FOR FORMINGSAME.

FIELD OF THE INVENTION

[0002] The present invention relates to a heat exchange device and, moreparticularly, to a finned heat exchange tube and to a process for itsfabrication.

BACKGROUND OF THE INVENTION

[0003] Heat exchange devices that include a fin helically wound around acylindrical tube are well known in the art. Typically, the fin and thetube are each formed of metal, and their interface must be efficientlyheat-conductive to ensure optimal heat transfer.

[0004] U.S. Pat. No. 2,152,331 to Shoemaker discloses a tubular body towhich is attached a helically wound fin flanked on either side byheat-conductive metal stabilizing strands that can be fastened by solderto the fin and tube, each of which is preferably formed from copper.

[0005] U.S. Pat. No. 4,960,170 to Carter is directed to a heat exchangerhaving a tube on which is helically wrapped, in a side by siderelationship, a thin fin made from a material of a higher coefficient ofexpansion than that of the tube and a wire from a material of the sameor a smaller coefficient of expansion than that of the tube.

[0006] In addition to devices formed by winding a fin around a tube, asdescribed in the Shoemaker and Carter patents, “low fin” heatexchangers, in which the fins are formed by machining a heavy walledtube, are commercially available. In such devices, the fin and centraltube are necessarily made of the same metal.

[0007] There is a continuing need for readily manufacturable heatexchange tubes, particularly of small diameter and with a low fin thatcan, if desired, be constructed of a material different from that of thetube. This need is met by the present invention.

SUMMARY OF THE INVENTION

[0008] The present invention is directed to a finned heat exchange tubethat comprises a metal cylindrical central tube having an outer surfaceand a metal fin helically disposed on and in thermally conductivecontact with the outer surface of the tube. The fin has a cross-sectionof trapezoidal shape that comprises a longer base and a shorter base,with the longer base being in contact with the tube outer surface.Alternatively, the fin can have a cross-section substantiallyrectangular in shape, having rounded corners and sides of longer andshorter dimensions perpendicular to one another, a side of the shorterdimension being in contact with the outer surface of the tube.

[0009] The invention is further directed to a process for forming a heatexchanger tube that comprises helically winding and securing a metal finon an outer surface of a metal cylindrical central tube. The fin, whichis in thermally conductive contact with the central tube, has across-section of trapezoidal shape that comprises a longer base and ashorter base, the longer base being in contact with the tube outersurface, or alternatively, a substantially rectangular cross-sectionwith rounded corners and sides of longer and shorter dimensionsperpendicular to one another, a side of the shorter dimension being incontact with the outer surface of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a perspective view of the finned heat exchange tube ofthe present invention.

[0011]FIGS. 2 and 3 are, respectively, side and end views of the finnedheat exchange tube.

[0012]FIG. 4 is a cross-sectional view of the heat exchange tube alongline A-A of FIG.3.

[0013]FIG. 5 is a detailed view of portion B of FIG. 4 that depicts thetrapezoidal cross-section of the fin.

[0014]FIG. 6 is a cross-sectional view of an alternative embodiment ofthe heat exchange tube wherein the fin has a substantially rectangularcross-section.

[0015]FIG. 7 is a detailed view of portion C of FIG. 6 that depicts thesubstantially rectangular cross-section of the fin The drawings are notnecessarily to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0016]FIGS. 1, 2, and 3 are various views of a finned heat exchange tube10 in accordance with the present invention. Tube 10 comprises a metalcylindrical central tube 11 and a metal fin 12 that is helicallydisposed on an outer surface 13 of tube 11. Tube 11 and fin 12 can beformed from the same metal or from different metals. For example,depending on the nature of the fluid flowing through tube 10, it mightbe desirable to make it from stainless steel, while constructing fin 11from copper for improved thermal conductivity. Tube 11 preferably isformed from copper, copper-nickel alloy, or stainless steel; fin 12preferably is made of copper or aluminum. It is important that theinterface 14 between tube surface 13 and fin 12 be efficientlyheat-conductive to ensure optimal heat transfer. To achieve good thermalconductivity at interface 14, fin 12 can be attached to tube surface 13by, depending on the metals employed and the intended use of heatexchange tube 10, adhering means such as solder or polymeric adhesive.Solder alternatives comprising polymeric adhesive pastes are availablefrom, for example, Emerson & Cuming Co., Billerica Mass.

[0017] Although the length and diameter of tube 10 and the dimensionsand pitch of helically wound fin 12 can be varied over a considerablerange, the present invention is particularly advantageous inapplications where small diameter heat exchange tubes with low fins aredesired, for example, for cooling a fluid such as oil. Referring to FIG.2, central tube 11 has an outside diameter D of, preferably, up to andincluding about one inch, more preferably, about ¼ inch, and fin 12 hasa height H of, preferably, up to and including about {fraction (3/16)}inch, more preferably, about {fraction (1/16)} inch.

[0018]FIG. 4 is a cross-sectional view of heat exchange tube 10 alongline A-A of FIG. 3. FIG. 5, a detailed view of portion B of FIG. 4,depicts the trapezoidal cross-section of fin 12.

[0019] As shown in FIG. 5, the trapezoidal cross-section of fin 12 has alonger base B₁ and a shorter base B₂, the longer base B₁ being incontact with tube outer surface 13. This trapezoidal configuration offin 12, which can be achieved by, for example, subjecting a wire ofround cross-section to shaping by suitable roll dies, provides increasedcontact between fin 12 and tube outer surface 13, thereby improving heattransfer performance.

[0020]FIG. 6 is a cross-sectional view of an alternative embodiment ofthe invention, a heat exchange tube 20 comprising a metal central tube11 and a metal fin 21 helically disposed on tube 11. As shown in FIG. 7,a detailed view of portion C of FIG. 6, the cross-section of fin 21 issubstantially rectangular in shape, with rounded corners and sides oflonger and shorter dimensions perpendicular to one another, a side ofthe shorter dimension being in contact with an outer surface 13 of tube11. The cross-sectional shape of fin 21 can be achieved by, for example,using a roll die to flatten a wire of round cross-section. Apart fromthe cross-sectional shape of fin 21, the characteristics of heatexchange tube 20, including its process of formation and mode ofoperation, are similar to those of heat exchange tube 10.

[0021] The invention has been described in detail for the purpose ofillustration, but it is understood that such detail is solely for thatpurpose, and variations can be made therein by those skilled in the artwithout departing from the spirit and scope of the invention, which isdefined by the following claims.

What is claimed is:
 1. A finned heat exchange tube comprising: a metalcylindrical central tube having an outer surface; and a metal finhelically disposed on and in thermally conductive contact with saidouter surface of said central tube, said fin having a cross-sectionselected from the group consisting of: a trapezoidal shape comprising alonger base and a shorter base, said longer base being in contact withsaid outer surface of said central tube; and a substantially rectangularshape having rounded comers and sides of longer and shorter dimensionsperpendicular to one another, a side of said shorter dimension being incontact with said outer surface of said tube.
 2. The heat exchange tubeof claim 1 wherein said fin cross-section has said trapezoidal shape. 3.The heat exchange tube of claim 1 wherein said fin cross-section hassaid substantially rectangular shape.
 4. The heat exchange tube of claim1 wherein said central tube and said metal fins are formed from the samemetal.
 5. The heat exchange tube of claim 1 wherein said central tubeand said metal fins are formed from different metals.
 6. The heatexchange tube of claim 1 wherein said central tube is formed from ametal selected from the group consisting of copper, copper-nickel alloy,and stainless steel.
 7. The heat exchange tube of claim 1 wherein saidfin is formed from a metal selected from the group consisting of copperand aluminum.
 8. The heat exchanger tube of claim 1 wherein said centraltube has an outside diameter of up to and including about 1 inch.
 9. Theheat exchanger tube of claim 8 wherein said central tube has an outsidediameter of about ¼ inch.
 10. The heat exchanger tube of claim 1 whereinsaid fin has a height of up to and including about {fraction (3/16)}inch.
 11. The heat exchanger tube of claim 10 wherein said fin has aheight of about {fraction (1/16)} inch.
 12. The heat exchanger tube ofclaim 1 wherein said fin is connected to said outer surface of saidcentral tube by adhering means.
 13. The heat exchanger tube of claim 12wherein said adhering means is selected from the group consisting ofsolder and polymeric adhesive.
 14. A process for forming a heatexchanger tube, said process comprising: helically winding and securinga metal fin on an outer surface of a metal cylindrical central tube,said fin being in thermally conductive contact with said outer surfaceof said central tube and having a cross-section selected from the groupconsisting of: a trapezoidal shape comprising a longer base and ashorter base, said longer base being in contact with said outer surfaceof said central tube; and a substantially rectangular shape havingrounded comers and sides of longer and shorter dimensions perpendicularto one another, a side of said shorter dimension being in contact withsaid outer surface of said tube.
 15. The process of claim 14 whereinsaid fin cross-section has said trapezoidal shape.
 16. The process ofclaim 14 wherein said fin cross-section has said substantiallyrectangular shape.
 17. The process of claim 14 wherein said central tubeand said metal fins are formed from the same metal or from differentmetals.
 18. The process of claim 14 wherein said central tube is formedfrom a metal selected from the group consisting of copper, copper-nickelalloy, and stainless steel, and said fin is formed from a metal selectedfrom the group consisting of copper and aluminum.
 19. The process ofclaim 14 wherein said central tube has an outside diameter of up to andincluding about one inch, and said fin has a height of up to andincluding about {fraction (3/16)} inch.
 20. The process of claim 19wherein said central tube has an outside diameter of about ¼ inch, andsaid fin has a height of about {fraction (1/16)} inch.
 21. The processof claim 14 wherein said fin is connected to said outer surface of saidcentral tube by adhering means selected from the group consisting ofsolder and polymeric adhesive.
 22. A finned heat exchange tubecomprising: a metal cylindrical central tube having an outer surface,said tube being formed from copper or stainless steel and having anoutside diameter of about ¼ inch.; and a metal fin helically disposed onand in thermally conductive contact with said outer surface of saidcentral tube, said fin being formed from copper and having a height ofabout {fraction (1/16)} inch, said fin further having a cross-sectionselected from the group consisting of: a trapezoidal shape comprising alonger base and a shorter base, said longer base being in contact withsaid outer surface of said central tube; and a substantially rectangularshape having rounded comers and sides of longer and shorter dimensionsperpendicular to one another, a side of said shorter dimension being incontact with said outer surface of said tube.